Coupled ferromagnetic structures include two ferromagnetic layers separated by a spacer layer. Thickness and composition of the ferromagnetic layers determine the effective properties of the structure. Thickness and composition of the spacer layer determine the type of interlayer exchange coupling that occurs between the two ferromagnetic layers.
Two variations of a coupled ferromagnetic structure are an artificial ferromagnet, and an artificial antiferromagnet. An artificial ferromagnet includes two ferromagnetic layers that are ferromagnetically coupled. That is, magnetic moments of the two ferromagnetic layers point in the same direction across the spacer layer.
An artificial antiferromagnet includes two ferromagnetic layers that are antiferromagnetically coupled across the spacer layer. That is, magnetic moments of one of the ferromagnetic layers point in an opposite direction of magnetic moments of the other ferromagnetic layer. The magnetic moments of the two ferromagnetic layers cancel on a macro scale. Net magnetic moment of the artificial antiferromagnet is determined by the difference in magnetic moments of the two ferromagnetic layers. If the two ferromagnetic layers have equal magnetic moments, the artificial antiferromagnet has zero net magnetization. If the two ferromagnetic layers have unequal magnetic moments, the artificial antiferromagnet has non-zero net magnetization.
The bottom ferromagnetic layer is formed on a seed layer. The seed layer provides proper texture (i.e., crystal orientation) for the bottom ferromagnetic layer. The proper texture provides high exchange coupling.
It would be desirable to form coupled ferromagnetic structures on amorphous materials. However, amorphous materials do not provide the proper texture for the bottom ferromagnetic layer.